In recent years, with the development of computer techniques, development of techniques related to equipment included in computers and peripheral equipment externally connected to computers have been advancing rapidly. A known example of such developing techniques is an information storage apparatus that includes a flat storage medium such as a magnetic disc, and stores information by writing the information to the storage medium.
Some types of information storage apparatuses record information on a storage medium and reproduce information from the storage medium (such recording and reproduction are referred to as “access” collectively, below) by bringing a head having a recording element and a reproduction element in contact with or closer to a surface of the storage medium. A hard disk device (HDD) is a representative example of these information storage apparatuses, and another known example is a magneto-optical disk (MO) device.
In such an information storage apparatus accessing a storage medium by using a head, multiple tracks are generally provided on the storage medium. These tracks are arranged in the radial direction concentrically around the disc center of the storage medium. The information storage apparatus performs the recording or reproducing of information by using the head in contact with or close to a surface of one of the tracks, while the storage medium is rotating. In this recording/reproducing system, the head needs to be moved to the track to be accessed (access target track). In the information storage apparatus accessing the storage medium by using the head, the head holding member which holds the head is moved above the storage medium, whereby the head is moved to the access target track.
In the recent information storage apparatus field, increasingly high recording density is achieved in storage media, leading to a decreasing trend in the distance between adjacent tracks (i.e., track pitch). To achieve highly accurate access, it is important to keep the head above the access target track with high accuracy without displacing the head from the track.
In general, in an information storage apparatus, the temperature inside the apparatus considerably changes along with the operation of the apparatus. Consequently, members and elements included in the information storage apparatus are deformed due to temperature change (accumulation of stress) in some cases. In particular, in the case of members and elements made of different kinds of materials, a portion where different materials are bonded together is highly likely to be deformed due to temperature change because these materials have different thermal expansion coefficients. When the extent of material deformation exceeds a certain critical limit, the materials instantaneously change their shapes (deformation release) to more stable shapes. This change causes a shock to the inside of the information storage apparatus. When the head accessing the storage medium is subjected to this shock, the head is displaced from the access target track, causing a problem of reduction in access accuracy. This problem is particularly serious when the head is displaced from the recording target track to a different track in the middle of information recording. This is because, in such a case, the information is erroneously recorded on the different track, and the information originally recorded on the different track is consequently deleted.
Recently, control systems have been proposed to avoid this problem (see Japanese Laid-open Patent Publication No. 2007-122798, for example). In such systems, temperature increase trend is monitored, and when the temperature rises above a predetermined threshold level, information recording is restricted to avoid reduction in information recording accuracy attributable to deformation release.
In the control system disclosed in Japanese Laid-open Patent Publication No. 2007-122798, however, information recording is restricted every time the temperature rises above the predetermined threshold level. This leads to another problem of reduction in working efficiency in information recording. Hence, further improvement is needed to achieve excellent access operation while avoiding reduction in access efficiency and reduction in access accuracy attributable to deformation release during access.